Reconfiguring grid-interfacing converters for power quality improvement

In this paper reconfiguration of grid-interfacing converters is proposed for power quality improvement. In addition to the traditional function of delivering energy between distributed sources and the utility grid, more flexible ancillary functions can be integrated into the control of grid-interfacing converters to both improve the power quality at the user side and the utility side. The potential for solving or improving various problems on different system levels is described in detail. Two three-phase four-leg inverters, together with DC microsources and loads, are employed to construct a general gridinterfacing system module. Through the redefinition of system functions, it is possible to achieve voltage unbalance correction, harmonic current compensation at the point of connection with the utility grid, protection of distributed generation systems from grid disturbances, and high quality voltage for sensitive loads under various utility grid situations. While the effect on helping the utility grid is small for a single module, a number of the modules put together could be pronounced. The Control scheme and validation results are presented in the paper